The present invention relates to water valves of the type intended for controlling flow of internal combustion engine coolant between the engine cooling passages and an exterior heat exchanger, for example, the heater core for a vehicle passenger compartment.
Heretofore, motor vehicle heater core water valves have typically either been manually actuated by a cable connected to a crank provided on the shaft of a butterfly plate type valve; or, the crank for the butterfly plate was connected by a link to a pressure operated diaphragm in a vacuum powered actuator.
Butterfly plate type water valves have proven to be generally reliable and low in manufacturing costs and thus have found widespread usage in automotive heater applications. However, butterfly plate type valves have the disadvantage of being quite non-linear in their flow control characteristics inasmuch as full flow of the valve occurs at about only one-quarter of the fully open position. This characteristic of butterfly type valves has resulted in difficulties in actuating the valve to obtain a predetermined amount of flow therethrough. Vacuum pressure actuators are limited in their size; and, thus the restricted diaphragm area limits the stroke resolution for pressure changes over the available range. Manual cable actuation has resulted in almost no useful modulation of the water flow.
Therefore it has been desired to provide an electrically operated heater core water valve to facilitate more accurate positioning of the valve member and therefore improved control over the flow of the coolant to the heater core. This is particularly desirable in a vehicle passenger compartment climate control system which is designed to provide automatic or thermostatically controlled temperature regulation in the passenger compartment. Heretofore electrically operated heater core water valves have employed a low voltage high RPM low torque motor driving a sector gear through a numerically high ratio gear reduction in order to provide the requisite torque needed to control the butterfly in the water valve and sufficiently fine resolution of the butterfly plate movement. Such servo motor operated speed reduced electric actuators have proven to be bulky and difficult to install on a water valve and in addition have resulted in relatively high manufacturing costs for the type of valve control desired.
Furthermore a motorized water valve employing a gear train does not permit automatic return of the valve to the open position in the event of electrical failure of the motor as is required in automotive passenger compartment heater applications.
Thus it has been desired to provide such a water valve for the passenger compartment heater core which will return to the fully open position in the event of failure of the servo motor.
In addition, it has long been desired to provide a simple, relatively low cost and reliable motorized water valve for controlling the flow to a vehicle passenger compartment heater core and to provide such a motorized valve which is compact and provides precision flow control.